Polyphenol recovery from sorghum bran waste by microwave assisted extraction: Structural transformations as affected by grain phenolic profile.

Sorghum milling waste stream (bran), contains diverse phenolic compounds with bioactive properties. The study determined the potential of microwave assisted extraction (MAE) to recover the bran phenolic compounds. Red, white, and lemon-yellow pericarp sorghum brans were subjected to MAE and phenolic yield and structural transformation vs conventional extraction (control) assessed by UPLC-MS/MS, Folin-Ciocalteu and Trolox equivalent antioxidant capacity methods. Phenols yield increased from 3.7-20.3 to 12.6-75.5 mg/g, while antioxidants capacity increased average 3.3X in MAE extracts vs controls. Hydroxycinnamic acids increased most dramatically (3.0-32X) in MAE extracts (0.08-2.64 to 2.57-8.01 mg/g), largely driven by release of cell-wall derived feruloyl- and coumaroyl-arabinose. MAE hydrolyzed flavonoid glycosides into aglycones, and depolymerized condensed flavonoid heteropolymers into flavanones, flavanols and (deoxy)anthocyanidins. Thus, MAE dramatically enhances yield of valuable phenolics from sorghum bran waste, but also alters the phenolic profile in ways that may influence their chemical and biological properties.

Interactions of 3-deoxyanthocyanins with gum arabic and sodium alginate contributing to improved pigment aqueous stability.

3-Deoxyanthocyanins (3DXA) are of interest as food colorants but readily precipitated in aqueous solutions, limiting their potential applications. This work investigated ability of gum arabic vs alginate to stabilize 3DXA in aqueous systems and mechanisms involved. Apigeninidin and luteolinidin, and sorghum extracts dominant in these compounds, API-EX and LUT-EX, respectively, were prepared in pH 3 and 5 polysaccharide solutions (0.5-1.0 g/L), and colloidal properties and 10-week stability measured. Alginate equally stabilized both pigments at pH 5 (75% retention), but only LUT-EX at pH 3 (65%); viscosity and H-bonding contributed to the effects. By contrast, gum arabic highly stabilized API-EX (100%, pH 5), but not LUT-EX. Gum arabic formed a stable complex with apigeninidin via hydrophobic encapsulation, but much weaker complex with luteolinidin due to its more hydroxylated B-ring. Structure of 3DXA is critical to its interaction with hydrocolloids, thus pigment profile must be considered when selecting stabilizing polysaccharides.

Effect of tannins on microwave-assisted extractability and color properties of sorghum 3-deoxyanthocyanins.

Sorghum derived 3-deoxyanthocyanins (3-DXA) are of growing interest as natural food colors due to their unique stability compared to anthocyanins, but are generally difficult to extract. Microwave-assisted extraction (MAE) can dramatically improve extraction efficiency of 3-DXA from sorghum tissue. However, condensed tannins common in some sorghums could impact MAE extractability and color properties of 3-DXA. The objective of this work was to determine how presence of condensed tannins affect MAE extractability, stability, and color properties of sorghum 3-DXA. Sorghums of varying 3-DXA profile and tannin content, as well as purified tannins, were subjected to MAE and pigment yield and profile, aqueous color properties and stability at pH 1 - 5 monitored over time using, UV-vis spectroscopy, colorimetry, and UPLC-MS. The relative yield of 3-DXA from tannin sorghums was higher (3 - 10-fold) after MAE than from non-tannin sorghum (2-fold). During MAE, condensed tannins underwent extensive oxidative depolymerization to anthocyanidins (cyanidin and 7-O-methylcyanidin), which caused the tannin-sorghum pigment extracts to have a redder hue (12-43H°) compared to the non-tannin pigment extract (58H°). The tannin-derived anthocyanidins transformed over time into xanthylium pigments, resulting in increased extract H°. Tannins enhanced both color intensity (pH 1) and stability (pH 3-5) of the 3-DXA over 14 days, indicating they acted as copigments. The presence of tannins in sorghum enhances MAE extractability of 3-DXA from sorghum tissue, and could also potentially enhance their functionality in aqueous food systems. However, the initial changes in extract hue properties due to tannin-derived anthocyanidins should be considered.

Application of a novel microwave energy treatment on brewers' spent grain (BSG): Effect on its functionality and chemical characteristics.

The effect of a new microwave energy treatment on brewers' spent grain (BSG) functionality and its application in a bakery product was evaluated. The physicochemical modifications of BSG were studied with special emphasis on the analysis of non-enzymatic browning reactions. Microwave treatment induced the formation of Maillard reaction products with a high antioxidant activity. The structure of these compounds was fully analyzed and it was concluded that melanoidins were formed by polymerization of furanose rings. Results indicated that chlorogenic acids were also reactants involved in the development of this reaction, leading to the formation of new bioaccesible compounds with important antioxidant activity. Although the addition of BSG in cookie formulations negatively affect their texture, this effect was successfully reduced when the microwave treatment was applied on BSG. This was associated to the disrupting effect that the microwaves had on BSG fiber, which significantly reduced its water absorption index (p ≤ 0.05).

Stability of 3-deoxyanthocyanin pigment structure relative to anthocyanins from grains under microwave assisted extraction.

Sorghum derived 3-deoxyanthocyanin (DXA) pigments are stable relative to their anthocyanin analogs, and are of growing interest in food applications. However, the 3DXA are poorly extractable from grain tissue. This work aimed to determine the relative stability and extractability of sorghum 3-DXA vs anthocyanins from maize and cowpea under microwave-assisted extraction (MAE). UV-Vis and UPLC-MS/MS spectrometry were used to characterize the properties. The 3-DXA remained structurally stable to MAE conditions up to 1200 W/100 °C/30 min. MAE increased sorghum 3-DXA yield 100% versus control (3100 vs 1520 mg/g). On the other hand, both maize and cowpea anthocyanins were unstable and rapidly degraded under MAE. Cell wall-derived ferulate esters were detected in sorghum and maize MAE extracts, indicating cell wall degradation occurred during MAE. Thus the enhanced extraction of 3-DXA under MAE was due to their structural stability, along with improved diffusion from cell matrix due to microwave-induced sorghum cell wall disruption.